This invention relates to a process for drying a product predominant in hexabromocyclododecane such that the formation of color bodies during drying is decreased.
Hexabromocyclododecane (HBCD) is a well known flame retardant agent, suitable for incorporation into various plastics especially polystyrene resins. As with other flame retardant additives, HBCD must fulfill several basic requirements such as melting range, color stability under processing conditions--or, in other words, it must remain colorless in order not to impart an undesired color to the article into which it is incorporated--and it may contain only a restricted amount of contaminants and impurities, such as bromides.
Preparation of HBCD by brominating cyclododecatriene (CDT) has been carried out in a number of different solvents, such as acetic acid, carboxylic acids, halogenated hydrocarbons, lower alcohols and mixtures thereof. The preferred solvent for the preparation of HBCD is a solvent comprising a lower alcohol.
Even when using a lower alcohol solvent, impurities are present in the HBCD product which tend to cause product discoloration. One such impurity is hydrobromic acid (HBr). Another is residual bromine. These impurities may be removed from the product or otherwise neutralized by treating the HBCD product with a basic solution such as K.sub.2 CO.sub.3, NaHCO.sub.3, CaCO.sub.3, NaOH, Na.sub.2 CO.sub.3, NH.sub.4 OH, NH.sub.4 HCO.sub.3, (NH.sub.4).sub.2 CO.sub.3, or gaseous ammonia prior to drying the product. Treatment may be performed before separation, during the separation, or subsequent to the separation of the HBCD product from a reaction mass wherein it is formed. While neutralization of the HBCD reduces the amount undesirable bromides in the dried product, a minor amount of HBr is released during the drying and/or packaging operation. Hydrogen bromide may be released during the drying operation by the decomposition of the moisture laden HBCD and subsequent reaction of the products of the decomposition with the moisture to form HBr and/or HBr which is entrained in the HBCD crystals may be released. When utilizing a dryer containing a significant quantity of ferrous metal, HBr reacts with the iron in the metal to form color bodies comprising iron bromide. These color bodies contribute an undesirable color component to HBCD product which in turn may cause discoloration of thermoplastic formulations using HBCD as a flame retardant. Thus, there is a need for a method to prevent the formation of color bodies in the HBCD product during drying and/or packaging.